1. Field of the Invention
The present invention relates to a flame-retardant synthetic resin composition. More particularly, the present invention relates to a halogen-free flame-retardant synthetic resin composition in which moldability (especially the parting property from a mold) is improved, the water resistance is enhanced, and the smoke-generating property is reduced.
2. Description of the Related Art
In general, synthetic resins have a light weight and are excellent in water resistance, chemical resistance, and electrical insulation characteristics and can be easily molded and processed. Therefore, synthetic resins are widely used as materials for electric appliances, materials for automobiles, construction materials, and the like. However, synthetic resins are generally defective in that they are easily burnt.
Accordingly, there have been proposed various methods for rendering synthetic resins flame-retardant. The method of internal addition of a halogen compound such as decabromodiphenylether or a halogen compound and antimony trioxide to synthetic resins is most widely adopted (see Japanese Examined Patent Publication No. 50-5103). Furthermore, there can be mentioned a method of addition of a metal hydroxide (Japanese Unexamined Patent Publication No. 50-34643, No. 50-133247, and No. 51-128194), a method of addition of a metal hydroxide and a polyphosphoric acid compound in combination (Japanese Unexamined Patent Publication No. 54-22450), and a method of addition of an inorganic compound (Plastic Compounding, 15, July-August, 1986). Moreover, there can be mentioned a method in which a polyhydric alcohol such as pentaerythritol is used in combination with a polyphosphoric acid compound, urea, melamine, or the like for rendering a synthetic resin flame-retardant by utilizing the heat-insulating action of an intumescent and carbonized layer at the combustion and inhibiting the conduction of heat to the substrate (Japanese Examined Patent Publication No. 61-47875 corresponding to U.S. Pat. No. 4,198,493 and Japanese Unexamined Patent Publication No. 60-36542).
However, these conventional techniques involve various problems. For example, in the case where a halogen compound is used, the hydrogen halide or the like generated by thermal decomposition corrodes the mold or the like at the molding or processing step, or, when a fire breaks out, evacuation is inhibited by generation of noxious odors or poisonous gas. Furthermore, it has recently been reported that there is a risk of formation of dioxine as a thermal decomposition product of halogen compounds [Environ. Sci. Technol., 20(4), 404-408, (1986)]. Especially in West Germany, there is observed a trend toward the control of use of halogen compounds. In the case where an inorganic compound such as a polyphosphoric acid compound or a metal hydroxide is used, the flame-retardant effect is low and the inorganic compound should be added in a large amount. Therefore, the specific gravity of the synthetic resin composition is increased and physical properties such as the strength and impact resistance are degraded.
Intumescent type flame-retardants comprising polyphosphoric acid compound, polyhydric alcohols and the like, which have been extensively studied and practically marketed, are defective in that since most of these compounds have a high hygroscopicity and polyhydric alcohols are generally water-soluble, the resin compositions comprising these compounds fail to have the high water resistance required for synthetic resins, the parting property from a mold is poor, and the molding efficiency is drastically reduced.
Various trials have been made to overcome these defects, but not satisfactory results have been obtained.